Electric hot water apparatuses are very popular nowadays. The known hot water apparatuses usually have a container for holding water as well as a thermal device for keeping the water hot.
Coffee lovers or tea lovers all know that the hotter the water used in making coffee or tea, the better the flavor brought out from it. However, it is very difficult for a conventional hot water apparatus to maintain the water hot for a considerable period of time, no matter how efficient its thermal device is. In other words, known hot water apparatuses cannot satisfy real coffee lovers and tea lovers.
In conventional hot water apparatuses, no matter how much water is in the water container, it requires a rather long time to heat up the water. This problem is mainly due to the drawbacks in conventional hot water apparatuses described below:
The heating principle of the conventional hot water apparatus is to heat water by high temperature produced by electric current passing through a resistance wire. To avoid the danger of electric shock to users due to electric conduction caused by the direct contact of water and resistance wire, the outer surface of the resistance wire must be treated with an insulating material. The overall structure of the heating unit is as shown in FIG. 1.
Generally, the resistance wire (1) is made in the form of a spiral and placed in the center of a metallic tube (3); between the resistance wire (1) and the metallic tube (3) is filled with electric insulating material (2). When electric current is supplied, the resistance wire (1) transmits heat to the water (4) through the insulating material (2) and the metallic tube (3). Since the heat conductivity of the resistance wire (1) is generally small, the effect of heat conduction of the resistance wire is not very ideal.
It can be observed from the above description of the heating unit in conventional hot water apparatuses that the heat conductivity of the resistance wire (1) is very low and cannot instantly heat up the water in the container. Furthermore, if the resistance wire (1) is designed to be longer in order to increase heat conduction, there must be a very long heating zone. Consequently, a large amount of electricity is required to heat the water and the hot water apparatus must be large enough to contain such a heating unit. As a result, such a hot water apparatus is very uneconomical and hardly a merchandizable product.
The above-mentioned problems have existed for a very long time, but no effective solution has been offered.
The theory of heating the tubular metallic body in a hot water apparatus by utilizing the electro-magnetic induction heating coil has been disclosed in the book entitled "Elements of Induction Heating" P. 23, FIG. 2.12, published in 1988 (Electric Power Research Institute, Inc., Palo Alto, Calif. 94303). The assembly theory of an electro-magnetic induction heating coil and tubular metallic body has also been disclosed in the book entitled "Induction Heat Treatment of Steel" P. 55, FIG. 3.3, published in 1986 (American Society for Metals, Metals Park, Ohio 44073). But, there are many difficulties in applying these theories in the making of hot water apparatuses, and up to now, no hot water apparatus adopting these theories has been successfully developed and sold on the market. The present invention has solved some of the difficulties, such as the problems of controlling the water temperature and instantly heating up the water to be flowed out to boiling point, among others, thus accomplishing a merchandizable hot water apparatus.